In Japanese Patent Laid-Open Publication No. 2004-138062 there is described a high-pressure fuel pump having a relief valve device, the relief valve device comprising a valve seat member having a central fuel passage and a seat surface formed around the central fuel passage, a valve element serving as a relief valve for being placed against the seat surface, and a spring member for pushing the valve element against the seat surface, the relief valve device being mounted to a body of the pump in such a manner that the spring member is positioned on the pressurizing chamber side.
However, in the above prior art, since the relief valve device is installed within the pressurizing chamber or within a passage leading to the pressurizing chamber, the volume of the pressurizing chamber substantially becomes large and the compression efficiency becomes lower.
More particularly, it suffices for the volume of the pressurizing chamber to be about 1 to 2 CC, but since the relief valve device is installed, the volume of the pressurizing chamber or the sum of the volume of the pressurizing chamber and that of the relief valve installed portion becomes 6 to 7 CC. Consequently, assuming that the stroke of a plunger piston (hereinafter referred to simply as “plunger”) within the pressurizing chamber is the same, the compression efficiency becomes lower.